Root-surface caries is likely to become an increasing health problem in the United States. Although fluoride in the drinking water appears to have some beneficial effect, the prevalence of the disease is still high in these fluoridated areas. There is a clear need for a well defined animal model that will develop root surface caries in a predictable and reproducible manner to study this disease and to explore its etiology and pathogenesis. The proposed study will determine the influence of specific diets and subsequently different carbohydrates on the development of root surface caries in rats infected with Streptococcus mutans and Actinomyces viscosus T-6. The time required for optimum development of root-surface caries will be observed to facilitate the conduct of future experiments. The transmission of Actinomyces from animal to animal will be studied because the phenomena involved could clearly be of importance in understanding infection by Actinomyces in humans. In addition the effect of a crude vaccine on transmission of infection will also be investigated. Results from this part of the study could eventually lead to an understanding of the surface antigens involved in the colonization of the gingival region by Actinomyces. Finally the effect of agents known to inhibit coronal caries will be examined and their effect on the population of actinomyces established. Humans who suffer from hyposalivation induced by salivary gland disease radiation or drugs are particularly prone to an unusual pattern of caries. Prevention of the disease imposes an unusually heavy burden on the patient thus the rate of compliance with preventive measures tends to be low. An animal model has not been established to systematically study the pathogenic phenomena involved in this disease and even more importantly to develop and screen methods for its prevention. By selective removal of salivary glands in rodents it will be possible to determine the effects of reduced salivary function or the almost complete absence of saliva on the development of caries.